Can't authenticate to trusted domain

I have a forest with two domains - D1 and D2; functional level is 2003. I built a new domain in a new forest - NewD; functional level is 2008. I need to be able to authenticate D1 users in NewD. DNS is set up with secondary zones for the other domain in each domain, and zone transfers are working. I made a two-way domain trust (NOT a forest trust) between the two domains, and it validated. My problem: I can authenticate in D1 with NewD users, but when I go to NewD, the D1 domain does not show up in the list of available domains, so I can't authenticate D1 users in the NewD domain.

Two questions: can I use stub zones instead of secondary zones in the DNS? and do I need to do a two-way FOREST trust for the authentication to work? Or maybe there is just some setting I am missing in my 2008 DCs that will allow the D1 domain to be seen. Any help is much appreciated.

Question 1:
Yes, you can use stub zones in DNS rather than secondary zones.

Question 2:
There is no reason to use a forest trust, I would expect the external domain trust that you have configured to work. Although the D1 domain is not in the domain list when logging onto a workstation in the NewD domain, it may be possible to authenticate a D1 user by specifying the username as <username>@D1, where D1 is the FQDN of the domain (not the NetBIOS name).

Would that work in setting permissions for resources as well? In both GPO and AD Users & Computers, I need to set permissions for administrators and users, and I haven't been able to because of the issue where the domain will not show up.

I cannot set permissions using groups without NewD active directory being able to see D1. Without that, I can't log in using my admin account from D1, and I can't administer the domain with my D1 credentials. Any idea why the AD can't see the D1 domain?

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